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<head>
    <meta charset="UTF-8">
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    <title>Document</title>
    <script>
        //接收用户输入的分数，根据分数输出对应的字母等级ABCDE.
        var num = prompt('请你输入分数');
        if (num >= 90) {
            alert('A');
        } else if (num >= 80) {
            alert('B');
        } else if (num >= 70) {
            alert('C');
        } else if (num >= 60) {
            alert('D');
        } else if (num >= 50) {
            alert('E');
        } else {
            alert('你真是个垃圾')

        }
    </script>
</head>

<body>

</body>

</html>